Pulse echo beacon transponder



WAS

July Q26, 1949. D. M. JACOB PULSE ECHO BEACON TRANSPONDER Filed Nov. l2, 1943 l `Parental July 26, 1949 PULSE ECHO BEACON TRANSPONDER lDon M. Jacob, Scotia, N. Y., assignor to General Electric Company, a corporation of New York Application November l2, 194, Serial No. 510,009

The present invention relates to apparatus for transmitting an echo pulse at an adjustable time after the receipt of a signal. Such apparatus, which may be termed a pulse echo beacon transponder, or more simply, an echo beacon, is useful in- Calibrating echo ranging radio locating equipment.

An object of my invention is to provide an improved echo beacon in which the delay interval is accurately adjustable.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims. My invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawing in which Fig. l is a circuit diagram, Fig. 2 illustrates the operation, and Fig. 3 is a modication for use in the circuit of Fig. l.

Referring to the drawing, there is shown an echo beacon used for Calibrating radio locating equipment having an antenna I connected to a transmitter 2 supplying pulses of radio Waves at the desired repetition rate and to a receiver 3 for echoes of the transmitted pulses. Associated with the receiver is suitable apparatus 4 for displaying the range of the objects reecting the echo pulses. Since the range of the reflecting .object determines the time of arrival o f the echoes, an echo beacon is obviously useful in calibrating the range scale of the display apparatus.

The echo beacon has an antenna 5 for picking up the pulses transmitted from the antenna I and for transmitting echo pulses simulating reections from an object at a range corresponding to the delay interval between the transmitted and echo pulses. The antenna is connected through transmission lines 6, 'I and a tuning stub 8 to the cathode-grid cavity of a reentrant cavity oscillator 9 tuned to the frequency of the transmitter 2. The oscillator 9 serves both as a detector for the pulses received by the antenna and as a`transmitter for the echo pulses.

During reception, and also during transmission, the positive half of each pulse is rectified, causing a negative pulse to appear at the anode I which is connected to the power supply through a resistance II and the secondary I2 of a transformer I3. This negative pulse is amplified in a resistance coupled amplifier I4 and appears as a positive pulse in the amplier output. The amplifier output is applied through a condenser I to a long delay multivibrator comprising discharge 6 Claims. (Ci. 343-18) devices IS and il, the device I1 being normally conducting and the device I6 being biased to cutoff by the current flowing in the common cathode resistor I8. The positive pulse from the amplifier I4, when applied to the grid I9 of the device IS,

causes the device I6 to conduct with the result that the voltage at the anode drops due to the current flowing through the resistance 2l. The voltage at the anode 20 is applied through a condenser 22 to the grid 23 of the device Il, driving the device I1 to cut-oil and causing an increase 'in the voltage at the anode 24 due to the interruption of the current through the resistance 25. The device I8 continues to conduct (and the device I'l remains cut off) until the condenser 22 discharges through resistance 26 to an extent suflicient to start the flow of current through the device I'I. At this time the voltage at the anode 24 suddenly drops due to the flow of current through the resistance 25 and the device I6 is biased to cut-01T by the flow of current through the cathode resistor I8. The condenser 22 and the resistance 26 are proportioned so that the interval during which the device I'l is cut 0E is longer than any interval during which an echo pulse can be transmitted from the oscillator 9. While the device I7 is cut olf, a positive pulse supplied to the grid I9 will have no effect since the device I6 is conducting when the device I'l is cut off.

The voltage at\the. anode 24 is fed through a differentiating circuit consisting of a condenser 21, an inductance 28, and a resistance 29. The addition of the inductance 28 to the condenser 21 and resistance 29, which comprise the conventional diierentiating circuit, -increases the rate at which the voltage at terminal 30 can rise and results in sharper positive and negative pulses at the leading and trailing ends of the voltage pulse appearing at the anode 24. The wave shape of the voltage at the terminal 30 is indicated directly above the wave shape of the voltage appearing at the anode, 24. The voltage at the terminal 30 is applied through a condenser 3| to a variable delay multivibrator comprising discharge devices 33 and 34, the device 34 being normally conducting and the device 33 being biased to cut- .off by the current owing through arm 36 of potentiometer 38. Upon the appearance of the positive pulse at the grid 33a of the device 33 (substantially coincident with the positive pulse at the output of amplier I4) the device 33 becomes conducting and the voltage at its anode 39 suddenly drops due to the current flowing through resistance 40. This sudden drop in volt- ;he anode 39 is adjustable by a slider 41 on the irm 36 of the potentiometer 38. The position of ;he slider determines the bias of the grid which n turn determines the value of current through ;he resistance 40. The interval during which the ievice 34 remains cut ofi' (the delay) vcan be Jaried from 2 microseconds up to something less ;han the delay of the preceding xed delay of the vibrator I6, I'I. This results in a positiveI square Nave pulse at the anode 44 having a width adustable by the setting of the slider 41.

The adjustment of the delay is made substan- ',ially independent of variations in the voltage supply by means of a resistance 48 connected 'rom the positive side of the voltage supply to ,he grid 33a and by the connection of the poyentiometer 38 in series with the cathode resistor i5. The connection lof the potentiometer in ieries with the cathode resistor tends to increase ihe bias on grid 33a faster than the increase in ,he supply voltage with the result that with in- :reasing supply voltage the grid 42 is driven nore positive and the delay increases. The addi- ;ion of the compensating resistance 48 has the )pposite e'ect on the bias of grid 33a, tending o decrease vthe delay with increasing supply voltage. The combination of the two effects )cmpensates for non-linearity of the device 33 and makes the delay independent of the voltage supply which may be unregulated. Since regulated voltage supplies are subject to changes rom day to day, the compensation is useful even avith a regulated voltage supply.

The output of the adjustable delay multivibrator, which appears at the anode 44, con- ;ists of a square wave voltage (the delay pulse) raving a duration determined by the setting of ',he slider 41 and having its leading edge triggered by the leading Aedge of the output of the )receding iixed delay multivibrator. A

The output of the adjustable delay multivibrator is connected to a condenser 49, opposite ;erminals of which are connected to the high iide of the power supply through a resistance 50 ind the primary 5I of a transformer 52. These Elements serve as a differentiating circuit causng positive and negative pulses in the trans- :'ormer primary 5I respectively at the leading ind trailing ends of the multivibrator output loltage. vThe transformer 52 is connected to a fegenerative pulser comprising a discharge defice 54 in'series with the primary 5I and a dis- :harge device 55 in series with the primary 56 )f the transformer I3. The positive pulse at the `eading end of the multivibrator output voltige is applied through the secondary 53 to grids i1 and 58 driving the grids from cut oil. to a nore negative bias. The negative pulse at the ,railing end of the .multivibrator output voltage irives the grids 51 and 58 positive causing a Flow of current `through the primary 5| which nduces a voltage in the secondary 53 increasng the positive bias on' the grids 51 and 58. The

creases the positive grid'bias and causes a further increase in current. As a result of this action, the devices 54 and 55 are rapidly driven to saturation. The induced voltage in the secondary 53 is applied to an artificial transmission llne 59 for providing a time delay equal to the desired pulse width of the pulser. The traveling 'voltage wave'on the transmission line starts down the line coincident `with the application of the positive voltage tothe vgrids 51 and 58 -and upon reaching the open end of the line (the end remote from' the grids 51, 58) is reflected with the same signV and upon arrival at the grids 51 and 58 biases the grids far beyond cut-off and abruptly terminates the flow of'current through the devices 54, 55. In the operationof the pulser. the

current through thedevices 54, 55 starts at zero,

abruptly increases to saturation, and continues at saturation for the length of time required for the voltage wave 'to travel twice the length of the .transmission line 59 and abruptlyreturns l to zero. The length `of the current pulse (l low of current through the device 54 is regenmicrosecond in the-present equipment) is controlled by the length of the transmission line. The current pulse through the device ilows through the primary 56 of the transformer I3 and causes a corresponding positive voltage pulse in the 'secondary I2 which is connected to the anode I0 of the oscillator 9. The oscillator 9 oscillates for the duration of the voltage pulse transmitting a simulated echo over the antenna 5 which is picked up by the antenna I and presented on the display 4 at a position corresponding to the delay. The oscillation of the oscillator 9 is also fed through the amplifier I4 to the grid I9 of the xed delay multivibrator device I6, but since the device is conducting there is no change due to the echo pulse. lThe fixed delay multivibrator prevents regeneration of the simulated echo pulse.

In the use of the' equipment the transmitted pulses of the radio locating equipment, indicated at line A, Fig. 2, are picked up by the antenna 5 of the echo beacon and are conducted tothe cathode-grid cavity of the oscillator 9. The echo beacon is usually located beside the locating equipment so that the pulses transmitted from the locating equipment appear substantially simultaneously in the cathode-grid cavity of the oscillator 9. The envelope of the oscillations in the cathode-grid cavity is shown in line B of Fig-2. The upper half of the envelope is rectified in the oscillator and applied through an amplier I4 to the fixed long delay multivibrator, causing firing of the multivibrator so as to produce the square wave voltage at the anode 24, indicated at line C in Fig. 2. The leading end of the output voltage of the fixed delay multivibrator is applied through a differentiating circuit 21, 28, 29 producing a positive pulse voltage which res the variable delay multivibrator. At the output of the variable 'delay multivibrator appears the square wave voltage indicated at line D in Fig. 2 having a length determined by the adjustment of the slider 41 varying from two microseconds to something less than the length of the fixed delay multivibrator output. The variable delay multivibrator output is applied to the pulse transformer 52 producing a positive pulse at the leading end and a negative pulse at the trailing end, indicated at line E in Fig. 2. The negative pulse res a pulser 54-59 applying a one-microsecond pulse through the transformer I3 to the anode I0 of the oscillator 9. `This causes the echo 4oscillations ndicated at in line B of Fig. 2. The echo oscillations are transmitted to the locating equipment producing a mark 8| on the range scale of the display apparatus li at a point corresponding to the delay of the echo'pulse'. Since the range of remote objects is determined by the time oi travel from the locating equipment to and from the reiiecting object, the echo pulse ofthe echo beacon simulates the echo from a remote object and provides a convenient method of checking the calibration of the range V scale of the locating equipment. During the transmission of the echo pulses the oscillations 60 appearing in the cathode-grid cavity of the oscillator 9 are rectied and fed through the amplifier It to the fixed delay multivibrator. However, this can have no eect since the echo pulses always arrive after the multivibrator has been iired. The use of the fixed delay multivibrator ahead of the variable delay multivibrator prevents regeneration of 'the' echo pulses which would otherwise result in the transmission of repeated echoes.

In` Fig. 3 is shown a modification for use in the circuit of Fig. 1, corresponding parts being indicated by the same reference numerals. In this modification, the transmission line t leading to the antenna 5 is replaced by transmission lines 62, B3 and an attenuator BB, and a switch 55 in the position shown in Fig. 1 to a contact B connected to a crystal detector 6l fed. from the end of the navaja connected in cascade between said receiving input circuit of ampliiier hl is moved from the .i

attenuator connected to the transmission line t2.

The balance of the Fig. 1 circuit is unchanged.

In the operation, the signal picked up by the antenna 5 is fed through vthe crystal El (instead of through the oscillator Q as in Fig. 1) to the amplier Ill. The echo pulse from the oscillator t is fed through the attenuator BQ to the antenna' 5 which reduces the intensity of the echo pulse to permit signal to noise measurements on the receiver 3. The echo pulse is also fed through Athe crystal'l, but has no eiect since the delay multivibrator l5, I l is not in `condition for firing.` It will be noted that the attenuator tl does not attenuate the received pulse and accordingly does not interfere with the operation of the echo pulse circuit. If the attenuator were merely inserted in the transmission line 6 of Fig. l without making other changes, the received pulse might be attenuated to a point at which it would not fire the delay multivibrator IS, ll andthe echo pulse would not be retransmitted.

While I have shown particular embodiments of my invention, it will be understood that many modificationsV may be made without departing from thespirit thereof, and I contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope of my invention.`

What I c laim'as new and desire to secure by Letters Patent of the United States is:

1. An echo beacon comprising a transceiver, a long delay multivibrator having its input con;- nected to the transceiver so as to be iired by the receipt of radio waves, a variable shorter delay multivibrator having its input connected to the output of the .first multivibrator so as to be fired by the leading end of the iirst multivibrator output whereby the variable delay multivibrator will be fired only once during the delay interval of the iirst multivibrator, and a puiser having its input.

lated echo pulseof radio waves.

' 2. Anecho beacon comprising an oscillator arranged to detect and transmit radio waves, a long delay multivibrator adapted when fired to pro duce a pulse of predetermined duration, means responsive to detection of radio waves to fire said long delay multivibrator, a variable shorter delay multivibrator adapted when-iired to produce a pulse of variable length, means responsive to the leading end of vthe pulse produced by said first multivibrator to fire said variable shorter delay multivibrator, and means excited by the trail/ing e'nd of the pulse produced by said variable delay multivibrator for pulsing the oscillatorso as to cause transmission of a' simulated eclfijgpulse oi? radio wavesiafter a delay interval deteiriiinedl by the adjustment of the variable delay -multivi brator. A

3. The combination, in an echo beacon, of an antenna circuit, transmitting and receiving means connected to said circuit whereby the receiving means responds to signals received in or transmitted by said antenna circuit, a pulser for said transmitting means, a pair of multivibrators means and said pulser, the iirst multivibrator including means responsive to a pulse received by said receiving means to generate a pulse having a fixed yperiod irrespective of any pulses received in said receivingI means during said ned period,

the second multivibrator including means respon sive to initiation of the pulse produced by the flrst multivibrator to produce a pulse of variable duration, and means responsive to termination of said pulse of variable duration to excite said pulser thereby to transmit a pulse through said antenna,

whereby said first multivibrator operates to preechoes of received pulses, a simulated echo pulse l being transmitted at a variable time after recep'- tion of the previously received pulse, said system comprising a pulse transmitter and receiver, and said receiver being responsive to pulses transm mitted yby said transmitter, the combination of means responsive to a pulse received in said receiver to produce a pulse in said transmitter upon elapse of a variable time after receipt of said pulse in said receiver, means to prevent operation of said last means in response to any pulse produced insaid transmitter in response to its own actuation, said preventing means comprising a multivibrator connected in circuit between said receiver and said pulse responsive means, said multivibrator including means responsive to a pulse received in said receiver to produce a pulse of fixed duration irrespective of any subsequent pulses received in said receiver, and means to supply said pulse of iixed duration to said pulse re-` sponsive means.

5. In combination, an antenna by which signal pulses are both transmitted and received, a transmitter connected to said antenna, means to pulse said transmitter thereby to supply pulses to said antenna for transmission thereby, a ,pulse-re sponsive circuit self operable from a normally receptive condition into a non-receptive condition fin response to a puise received in said antenna 7 non-receptive condition for a period not less tha said interval.

8. In a system for artificially transmitting echoes of received pulses, a simulated echo pulse being transmitted at a variable time after recep-v tion of the previously received pulse, said system comprising a pulse transmitter and receiver, land said receiver being responsive to pulses trans- .mitted by said transmitter, the combination oi means actuated upon receipt of and by a pulse received iny said receiver to producel a pulse in' said transmitter upon elapse of a variable. time after receipt of said pulse in said receiver, and time delay Ameans interposed between said receiver and said pulse responsive means operative after actuv ation of said pulse responsive means by said received pulse to prevent the pulsing of said pulse responsive means during a time interval following said received pulse oinot less than said variable time.

DON M. JACOB.-

REFERENCES CITED v 'The following references are of record-in the ille of this patent:

g www 

